Schnorr issue

[MateriaIistGuy]

Hi! I want to apologise in advance for perhaps such a simple question for you (judging by the topics discussed here). I'll briefly describe the problem. I receive from API raw PSBT with input indexes to be signed taproot. I have done all possible checks: signhash and taproot calculation, no changes in BASE64 processes, empty symbols, Shnorr validity and that BASE64 is exactly 64 (not 64 + 1), but I get the same error every time. I tried to find some information on BTC stack, but there was very little, and when I asked a question no one understood what the problem was either. I swear I don't understand the problem.

Logic: 1. Receive psbt and decode -> Sign inputs (I don't finalise, the server does) using Default method (ALL the same result)-> encode in Base64 -> return partially signed PSBT to server.

I get the "Invalid Schnorr" error every time by server. You see, if you compare script PSBT and output psbt, they are 99% identical except for Shnorr (field unknown 13). I've attached a screenshot to show the difference.

1. I thought the problem might be in the formats for the server, but Bitcoin cli analyse returns an ‘updater’ status for my script output:

{
    { ‘result’: {
        { ‘inputs’: [
            {
                ‘has_utxo": true,
                ‘is_final": false,
                { ‘next’: { ‘updater’.
            },
            {
                ‘has_utxo": true,
                ‘is_final": false,
                { ‘next’: { ‘updater’.
            }
        ],
        ‘estimated_vsize": 286,
        ‘estimated_feerate": 6.0e-5,
        ‘fee": 1.716e-5,
        ‘next": { ‘updater’.
    },
    ‘error": null,
    ‘id": null
}

2. Although if I sign via Unisat or any other extension wallet - it will return:

{
    ‘result": {
        { ‘inputs’: [
            {
                ‘has_utxo": true,
                ‘is_final": false,
                { ‘next’: { ‘updater’.
            },
            {
                ‘has_utxo": true,
                ‘is_final": false,
                { ‘next’: ‘finalizer’.
            }
        ],
        ‘fee": 1.716e-5,
        ‘next": { ‘updater’
    },
    ‘error": null,
    ‘id": null
}

Code (format via GPT to make more readable, result the same as orginal):

package main

import (
	"bytes"
	"encoding/base64"
	"fmt"
	"strings"

	"github.com/btcsuite/btcd/btcec/v2/schnorr"
	"github.com/btcsuite/btcd/btcutil"
	"github.com/btcsuite/btcd/btcutil/psbt"
	"github.com/btcsuite/btcd/txscript"
	"github.com/btcsuite/btcd/wire"
)

func main() {
	wifKeyStr := "WIF"
	psbtBase64 := "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"
	cleanPSBTBase64 := cleanBase64(psbtBase64)

	psbtBytes, _ := base64.StdEncoding.DecodeString(cleanPSBTBase64)
	packet, _ := psbt.NewFromRawBytes(bytes.NewReader(psbtBytes), false)

	prevOutFetcher := txscript.NewMultiPrevOutFetcher(nil)
	for i, input := range packet.Inputs {
		if input.WitnessUtxo != nil {
			prevOutFetcher.AddPrevOut(packet.UnsignedTx.TxIn[i].PreviousOutPoint, &wire.TxOut{
				Value:    input.WitnessUtxo.Value,
				PkScript: input.WitnessUtxo.PkScript,
			})
		}
	}

	inputToSign := 1
	if len(packet.Inputs[inputToSign].TaprootInternalKey) > 0 {
		sigHashes := txscript.NewTxSigHashes(packet.UnsignedTx, prevOutFetcher)
		pkScript, _ := getInputScript(packet, inputToSign)
		amount, _ := getInputAmount(packet, inputToSign)

		taprootInternalKey := packet.Inputs[inputToSign].TaprootInternalKey
		wifKey, _ := btcutil.DecodeWIF(wifKeyStr)
		publicKeyFromWIF := schnorr.SerializePubKey(wifKey.PrivKey.PubKey())

		if bytes.Equal(taprootInternalKey, publicKeyFromWIF) {
			sighashType := txscript.SigHashDefault
			sighash, _ := txscript.CalcTaprootSignatureHash(sigHashes, sighashType, packet.UnsignedTx, inputToSign, txscript.NewCannedPrevOutputFetcher(pkScript, amount))

			signature, _ := schnorr.Sign(wifKey.PrivKey, sighash)
			serializedSig := signature.Serialize()

			packet.Inputs[inputToSign].TaprootKeySpendSig = serializedSig
		}
	}

	signedPsbtBase64, _ := packet.B64Encode()
	fmt.Printf("Signed PSBT (Base64): %s\n", signedPsbtBase64)
}

func cleanBase64(s string) string {
	return strings.Join(strings.Fields(s), "")
}

func getInputScript(packet *psbt.Packet, idx int) ([]byte, error) {
	input := packet.Inputs[idx]
	if input.WitnessUtxo != nil && len(input.WitnessUtxo.PkScript) > 0 {
		return input.WitnessUtxo.PkScript, nil
	}
	if input.NonWitnessUtxo != nil {
		prevTx := input.NonWitnessUtxo
		outPoint := packet.UnsignedTx.TxIn[idx].PreviousOutPoint
		if int(outPoint.Index) >= len(prevTx.TxOut) {
			return nil, fmt.Errorf("Invalid outpoint index %d for input %d", outPoint.Index, idx)
		}
		return prevTx.TxOut[outPoint.Index].PkScript, nil
	}
	return nil, fmt.Errorf("PkScript not found for input %d", idx)
}

func getInputAmount(packet *psbt.Packet, idx int) (int64, error) {
	input := packet.Inputs[idx]
	if input.WitnessUtxo != nil {
		return input.WitnessUtxo.Value, nil
	}
	if input.NonWitnessUtxo != nil {
		prevTx := input.NonWitnessUtxo
		outPoint := packet.UnsignedTx.TxIn[idx].PreviousOutPoint
		if int(outPoint.Index) >= len(prevTx.TxOut) {
			return 0, fmt.Errorf("Invalid outpoint index %d for input %d", outPoint.Index, idx)
		}
		return prevTx.TxOut[outPoint.Index].Value, nil
	}
	return 0, fmt.Errorf("WitnessUtxo or NonWitnessUtxo not found for input %d", idx)
}


OUTPUT:

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
Calculating Taproot address...
Taproot Address: bc1p38pg0767rhujdn569lug887yea73rn7vpwz546y7czzcptql9caq6cafwt
TapKeyBytes: 89c287fb5e1df926ce9a2ff8839fc4cf7d11cfcc0b854ae89ec08580ac1f2e3a
2024/11/27 12:13:42 Taproot Address: bc1p38pg0767rhujdn569lug887yea73rn7vpwz546y7czzcptql9caq6cafwt
Public Key (Hex): ad17b47056ee8c7257aefb92fcc82f9ea4691c748b90000e3df2ba6471403d7b
Decoding PSBT...
PSBT successfully decoded.
Parsing PSBT...
PSBT successfully parsed.
Creating MultiPrevOutFetcher...
Adding previous output for input 0
Adding previous output for input 1
MultiPrevOutFetcher successfully created.
Signing input 1...
Input uses Taproot.
Creating TxSigHashes...
TxSigHashes successfully created.
PkScript: 512089c287fb5e1df926ce9a2ff8839fc4cf7d11cfcc0b854ae89ec08580ac1f2e3a
Amount: 55470
TaprootInternalKey of input 1: ad17b47056ee8c7257aefb92fcc82f9ea4691c748b90000e3df2ba6471403d7b
Public key from WIF: ad17b47056ee8c7257aefb92fcc82f9ea4691c748b90000e3df2ba6471403d7b
The signing key matches the TaprootInternalKey of the input.
Calculating sighash...
Sighash: 92aec029f002090d7621fffce4ebac7ff333d971e832db3980bb93112cb851ce
Creating signature...
Signature: 98dcfc29a85bc89ed35a86fa8073d5708ea93e095f4171b65c72ed12227d537a849b539ef6f9b845aeef61ff0bd4e94b664981e14a29e2443ddca98ecb9360f3
Signature for input 1 added.
Serializing signed PSBT...
Signed PSBT (Base64): 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

PSBT MY Script output:
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

Wallet extension PSBT:
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

Raw PSBT (input psbt fot scirpt and extension):
cHNidP8BAPwCAAAAAgupxw+/SJhtowTzcr1wx9c/uanFKaJ3yU3J6UKjMTMzlAEAAAD/////Q9g6nnkQbdroR/sr2jeNqZ9nlZbVuqSNdjakxTxLgYADAAAAAP////8ETQEAAAAAAAAiUSCJwof7Xh35Js6aL/iDn8TPfRHPzAuFSuiewIWArB8uOmGDAAAAAAAAIlEgsxHYe7mlcSxOwOnapg4WHRT5UuB+vWF8uMz6Oxu5Bf9DAgAAAAAAABYAFAnkWBtaeW/v/BxPBmkgboAct6nrVkwAAAAAAAAiUSCJwof7Xh35Js6aL/iDn8TPfRHPzAuFSuiewIWArB8uOgAAAAAI/AJtZQNzaWdAvHgNmehOZ6jBZiu5ckCncLnVeViAr3PlKIgR2v8NPzhW/OXpu8oaK4b3bgRIL/qrMT5WlpgdybZGXVaAxSJVIwv8Am1lBnNpZ2V4cAhCeTbOW+ZAAAABAStNAQAAAAAAACJRIDCs9kAJfdTiQei7Cf+RSH3Cwr5oxFjNj27APixQD2L4ARcgc+G1jBTUGzdWX447VOZ6zEec2eeffMqg8KTrQ6plriIAAQErrtgAAAAAAAAiUSCJwof7Xh35Js6aL/iDn8TPfRHPzAuFSuiewIWArB8uOgEXIK0XtHBW7oxyV677kvzIL56kaRx0i5AADj3yumRxQD17AAAAAAA=

[guggero]

Things look correct, as far as I can tell.
Perhaps an issue with the pk script and amount.
Why don't you just use sighash, _ := txscript.CalcTaprootSignatureHash(sigHashes, sighashType, packet.UnsignedTx, inputToSign, prevOutFetcher)?
Then you don't need getInputAmount and getInputScript.

[MateriaIistGuy]

Yes, thank you. Already added everything I could as my head was spinning. I made debug logs for PSBT formation, everything seems to be correct, but same invalid Shnorr and:

"has_utxo": true,
"is_final": false,
"next": "updater" (not expected finilizer status)

I tried to understand why expansion wallets do it the way they should, but I didn't find anything. I think I saw only Unisat wallet (I may be wrong), but I didn't understand how it does it with the same execution steps